Dinesh's photos with the keyword: On Being Certain

At a presynaptic terminal (top) small vesicles twenty or thirty nanometers in diameter filled with neurotransmitter molecules are waiting. Arrival of an action potential (or spike) induces a fusion of the membrane with some of the vesicles so that a neurotransmitter can diffuse into the synaptic cleft and reach receptors (not shown) at the other side, which then open ion channels they are attached to. A synapse becomes more or less efficient, like when vesicles get bigger or smaller, or more or fewer release sites become available, while postsynaptically the ion channels may increase or decrease iun number and stay open during a longer or shorter period of time. So most, though not all, of the active processes are happening in the pre- and postsynaptic membrane. The result is called learning. (Image courtesy of Synaptic Corporation Aurora, Colorado, United States; www.synapticuse.com)